Breakwater



BREAKWATER Filed Sept. 9, 1938 1NVENTOI?.

ATTOEN EY.

Patented Jan. 19, 1943 BREAKWATER- Harmen Streefkerk, Curacao, Netherlands West Indies Appiication September 9 1938, serial No. 229,044

In the Netherlands October 12, 1937 y v 3 Claims.

Breakwaters, piers, jetties, wave breakers and similar structures having substantially vertical walls favorably compare with barriers with flat slopes, since they allow ships to lie alongside for discharging and taking cargo, in addition to requiring an appreciable smaller quantity of materials. Ordinarily, they are composed of suitably keyed blocks set one directly above another and provided with a monolithic capping so as to form a solid superstructure, which is founded on a layer of rubble stone for evenly transmitting .the weight cf Vthe superstructure to the sea bottom. In many cases, caissons are used instead of superposed blocks.

When such a breakwater or the like is exposed to breaking waves, the outerrtoeand the inner toe of the solid superstructure exert on the rubble base so-called toe bearing pressures, the magnitude of which considerably exceeds that of the uniform bearing pressure exerted on the foundation in absence of waves. Consequently, the settlement of the rubble base below .the upright faces of the solid superstructure exceeds that in the central region, so that the surface of the rubble base assumes a more or less cylindrical shape. Owing to .this deformation, the superstructure begins to roll under the action of the waves to which it is exposed, i. e., to list alternately to the one and to the other side, whereby .the foundation is locally subjected to heavy overloads alternating with zero loads.

As soon as this rolling action sets up, the rubble mound has also to take up the kinetic energy of the rocking superstructure, so that the curvature of .the aforesaid cylindrical surface, and, consequently, the amplitude of the rocking movement is increased. Owing thereto, and also to the fact that in its extreme positions the superstructure is only partly supported by the foundation, the rubble stone is liable to be crushed and scoured out, or deposited in existing cavities, thereby bringing about the degradation of the mound. Moreover, and unless the rubble base has an exceptionally great Ithickness, the bearing capacity of the sea bottom, assuming the same to be sandy, is surpassed, whereby shearing of the rubble base is likely to occur. Thus, the superstructure gradually subsides and sometimes breaches, as owing to the great difference between the Water pressures on both sides it is increasingly subjected to undermining forces, i. e., to the scouring effect of lateral running water, whereby the rubble base is eroded.

In accordance with my present invention, which has for its object to avoid the aforesaid rawbacks, the foundation, as viewed in crosssectional elevation, comprises two plates, one for each toe of the solid superstructure, said plates being so disposed as to be loaded substantially centrally, both when the sea is calm, and when the Wave pressure, .to which the breakwater is exposed in either direction, reaches its maximum value.

rSaid plates can be so dimensoned as to always exert substantially equal and positive specific pressures on the rubble mound. Thus,

the settlement of the rubble base will be controlled and rendered uniform through the full width of the superstructure, so that the latter has no tendency to list.

My novel mode of founding the superstructure of barriers of the type referred vto prevents the superstructure from rolling Both foundation plates always exert positive pressures on the rubble mound, the bearing capacity of the sea bottom is nowhere surpassed, and the rubble base is prevented from shearing. Moreover, the breakwater is protected from lateral running water.

' The somewhat higher expense involved in the construction of a breakwater in accordance with my invention is overbalanced by the following savings:

(a) As the settlement of the rubble base is small and the superstructure is prevented from swaying, the expenditure on maintenance is rela tively low, both during construction and after completion.

(b) Owing to the smallness of the Vsettlement it is not necessary to allow several months to lapse between the raising of the superstructure out of water, and the placing of the monolithic deck or capping, in which case the non-capped and thereby relatively weak superstructure would be liable to damage by gales during said period.

(c) The chance for the breakwater to breach, partly or wholly, during a hurricane is greatly diminished, if not entirely abolished.

The drawing shows, by way of example only, a breakwater constructed in accordance with my novel principles. In said drawing:

Fig. 1 is a cross-sectional elevation of the breakwater, whereas Fig. 2, which is a cross-sectional elevation, drawn to a larger scale, of the solid superstructure and of the foundation plate, shows a diagram of the forces generated by the wave pressures in either direction.

The superstructure is composed of blocks I, suitably keyed by reinforced concrete columns 2 and or" a monolithic capping 3. The bottom block 4 of the superstructure is supported by the sections 1 and 8 of the foundation plate only through its toes 5 and E, respectively. Said sections are provided, on their top faces, with integral checks 9 and ID, respectively, which positively prevent any transverse shifting movement of the superstructure. The section I I of the foundation plate serves the purpose of consolidating the rubble stone intermediate the sections 'I and 8. The foundation plate, which further comprises covering sections I2 forming aprotective apron for the rubble mound I3, is sunk on a prepared levelled bed of said mound.

The forces acting on the superstructure are: (1) the weight of the superstructure in water, represented by G, (2) the wave pressure on the sea side Z, and (3) the wave pressure on the harbour side H. The maximum values of said pressures are represented in direction and magnitude by A and B, respectively, it being understood that A considerably exceeds B. The resultant of A and G is represented by C, that of B and G by D. Said resultants, as transmitted to the points or toes 5 and 6 in which the superstructure is supported, are represented by C5-Cs, and by Ds-De, respectively.

The points wherein the forces D5, C6 intersect the bottom faces of the plate sections 1 and 8 are designated by I4 and I5, respectively, and ,i

these points are located in the centres of said faces. If A and B decrease to zero, the points I4 and I5 will shift inwardly, but only through very small distances, so that they remain substantially in the centres of the plate sections I and 8, respectively. It follows that the sections 'I and 8 will always be loaded substantially centrally. The dimensions of said sections can be so chosen that the vertical components of Ds and Cs cause both sections to exert equal specie pressures on the rubble base I3.

As far as my invention is concerned, the construction of the solid superstructure is immaterial. Caissons may be employed in the building of the superstructure, and in that case the caissons may be so constructed that their side walls project a little below their bottom so as to actually constitute toes corresponding to the toes 5 and 6 shown in the drawing. Furthermore, the superstructure may be founded by a levelling layer of rubble stone or the like directly on the sea bottom, instead of on a mound having sloping sides.

What I claim is:

1. A sea barrier, such as a breakwater, mole, jetty or a wave breaker comprising an upwardly extending superstructure, a bottom block for said superstructure, toes downwardly projecting from said bottom block, a substantially horizontal foundation plate for each of said toes, said foundation plates being arranged in spaced relation and transversely of said bottom block, and a plate section interposed between said foundation plates lling the space therebetween, said foundation plates being engaged by said toes, respectively, at points thereof so as to substantially centrally `transfer to said foundation plates, respectively, the load exerted by the weight of said superstructure and by sea water forces acting thereon.

2. A sea barrier, such as a breakwater, mole, jetty or a wave breaker comprising an upwardly extending superstructure, a bottom block for said superstructure, toes downwardly projecting from said bottom block, a substantially horizontal foundation plate for each of said toes, said foundation plates being arranged in spaced relation and transversely of said bottom block, a plate section interposed between said foundation plates filling the space therebetween, said foundation plates being engaged by said toes, respectively, at points thereof so as to substantially centrally transfer to said foundation plates, respectively, the load exerted by the weight of said superstructure and by sea water forces acting thereon, and a check protruding from each of said foundation plates and positioned beyond said toes, respectively, preventing transverse shifting movement of said superstructure on said foundation plates.

3. A sea barrier, such as a brealrwater, mole, jetty or a wave breaker comprising an upwardly extending superstructure having substantially vertical walls, spaced extensions downwardly projecting from said superstructure, and a separate substantially horizontally extending plate means positioned underneath each of said extensions and laterally projecting beyond said superstructure, each extension substantially centrally engaging its plate means whereby the load exerted by the weight of said superstructure and by sea water forces acting thereon is substantially centrally transferred to said plate means, respectively.

HARMEN STREEFKERK. 

